1. Field of the Invention
The present invention relates to a surface illumination apparatus in which the polarization characteristic of light is utilized, and a liquid crystal display provided with this surface illumination apparatus. Particularly, it relates to a surface illumination apparatus in which the polarization characteristic of a laser beam is utilized by using a laser light source as a source for light emission, and a liquid crystal display provided with this surface illumination apparatus.
2. Description of the Background Art
A liquid crystal display displays an image by controlling the transmission quantity of a beam of light projected from its rear surface, using an electro-optical effect by the orientation of liquid-crystal molecules. In general, this method requires a surface illumination apparatus called a backlight unit which is formed by a vacuum fluorescent display and the like. In such a liquid crystal display, in recent years, its screen size has become increasingly large, and even a 50-inch size display for television has been put to practical use. At the same time, however, its power consumption increases as its size is larger, and thus, the necessity arises for the development of an art of lessening the power consumption.
As described above, a liquid crystal display is not a self-light-emission display, and thus, the power consumed in a light source used for a backlight unit is greater than the power consumed in a liquid-crystal display panel. In order to reduce the power consumption of the backlight-unit light source to a low level, a light source capable of emitting light efficiently needs to be used, as well as the backlight-unit illumination light needs to pass efficiently through the liquid-crystal display panel. These are serious problems to be solved.
As such a light source, instead of a conventionally-used vacuum fluorescent display, a light-emitting diode or a laser light source has been considered. A light-emitting diode is already put to practical use. However, numerous light-emitting diodes or laser light sources are necessary for obtaining illumination light which has a large area and a high intensity. This increases the power consumption of such light sources and raises the cost of mounting many such devices. Besides, in a backlight unit provided with a light-emitting diode, the range of color reproduction is enlarged to thereby enhance the picture quality. However, a large number of light-emitting diodes hinder an adequate reduction in the power consumption.
Therefore, as an important task, an art for a backlight unit has to be developed for reducing the number of light sources used in the backlight unit, as well as not wasting the illumination light thereof and allowing this illumination light to efficiently pass through a liquid-crystal display panel. In a liquid crystal display, illumination light projected from a backlight unit passes through the polarizing plate of a liquid-crystal display panel. Thereby, only half the quantity of light radiated from a light source is effectively used in practice. Hence, if illumination light polarized in advance passes through the polarizing plate, the illumination light from the backlight unit could be utilized at a higher light-usage efficiency.
On the basis of this approach, a collimating plane light source is disclosed (e.g., refer to Japanese Patent Laid-Open Publication No. 2002-169480). This collimating plane light source is configured by: a laser light source which has a predetermined emission width; a reflecting member which divides light emitted from the laser light source into a plurality of beams and reflects each beam in parallel with each other in a predetermined direction; and a deflecting member which includes a plurality of half mirrors that reflect each beam reflected by the reflecting member in a substantially perpendicular direction to its parallel plane and transmit the rest.
In this method, there is no need to provide a large number of laser light sources. Hence, a high-definition collimating plane light source can be obtained using a simple configuration with a single laser light source. Besides, a display element and a display unit with a high definition can be obtained which have less of a viewing angle dependency and require no backlight such as a fluorescent lamp and no color filter.
Furthermore, a polarization illumination apparatus is disclosed (e.g., refer to Japanese Patent Laid-Open Publication No. 8-304739). This polarization illumination apparatus includes: a light source portion in a lamp which emits light polarized in random directions; a first lens plate formed by a plurality of rectangular collective lenses for forming a plurality of secondary light-source images; and a second lens plate which is arranged near the formation position of the plurality of secondary light-source images and is provided with a polarization-separation prism array having a collective-lens array, a polarization beam splitter and a λ/2 phase-difference plate, as well as an emission-side lens.
Thereby, the first lens plate forming an integrator optical system generates minute secondary light-source images, and at this stage, polarized illumination light is separated. This helps restrain an optical path from spreading spatially when polarized illumination light is separated. Therefore, even if a polarization-conversion optical system is provided, the polarization illumination apparatus becomes smaller and useful for a liquid crystal projector.
Moreover, an image display including a lamp array as a light source according to the above described polarization illumination art is disclosed (e.g., refer to International Publication Pamphlet No. 99/49358). This image display is designed to make good use of light from the light source at a high light-usage efficiency. Simultaneously, an illumination apparatus is formed in one body to thereby make the image display smaller.
In the collimating plane light source disclosed in Japanese Patent Laid-Open Publication No. 2002-169480 described above, a beam of light emitted from the single laser light source is deflected by the reflecting member and is reflected in the substantially perpendicular direction by the deflecting member. However, no account is taken of control of the polarization of the laser beam. Since the polarization of the laser beam is not controlled, the laser beam is not uniformly polarized.
In the polarization illumination apparatus disclosed in Japanese Patent Laid-Open Publication No. 8-304739 described above, a beam of light emitted from the lamp is uniformly polarized by the plurality of lenses, the polarization-conversion optical system and the lens array. Then, it is enlarged and emitted. Thereby, the shape of the emitted beam becomes larger in the emission direction, thus making it harder to reduce the thickness of a surface illumination apparatus for a flat large-screen liquid-crystal display. Neither a disclosure nor a suggestion is given about information on such a thinning art.
The image display given in International Publication Pamphlet No. 99/49358 described above requires the array light source having a plurality of lamps arranged two-dimensionally. This causes the problem of increasing its power consumption and raising the cost of parts. In addition, a thin-and-flat large-screen image display is difficult to realize using the image display having this configuration. Besides, neither a description nor a suggestion is given about preserving a polarized laser beam using a laser light source and a light guide plate and allowing the uniformly-polarized laser beam as a parallel beam from the thinner light guide plate to irradiate a liquid crystal panel.